1. Field of the Invention
The present invention relates to electrodeposited copper foils, and more particularly, to an electrodeposited copper foil suitable for use in a printed circuit board and rechargeable and discharge batteries.
2. Description of Related Art
A printed circuit boards (PCB), used as a critical equipment for various types of electrical devices and products, is capable of carrying an electronic element and being connected to an electrical circuit, such that a stable operating environment is provided. PCBs have a broad range of applications, including in the consumer, industry and national defense sectors. Moreover, the fabrication of a PCB involves the assembly of the industries of materials, electricity, mechanics, chemistry, and optics, and thereby sufficiently demonstrating the importance of PCBs to the economical development.
However, in the fabrication of a PCB, a copper foil is adhered onto a substrate, and then made into a circuit pattern. Nodules are usually formed on a surface of a copper foil, In the past, the ratio of line width/line interval is larger. However, as the manufacturing of lighter, thinner, shorter and smaller electronic products gradually become a trend, the requirement for the line width/line interval ratio gets stricter, i.e., the ratio has reached 2 mil/2 mil (i.e., 50 μm/50 μm), or even 1 mil/1 mil (i.e., 25 μm/25 μm). Therefore, even a very small nodule would cause short circuit in a PCB substrate, such that the nodules on a surface of a copper foil need to be removed.
Moreover, the need for lithium ion secondary batteries in the modern society is also increasing. A lithium ion secondary battery must have safety in use and a long battery life, in addition to having a good discharging property. Hence, the process of fabrication of a lithium ion secondary cell must be more rigorous and delicate.
The structure of a lithium ion secondary cell is obtained by reeling a positive electrode pole piece, a separator, and a negative electrode pole piece together, placing them into a container, injecting an electrolyte, and sealing to form a battery, wherein the negative electrode pole piece is composed of a negative electrode collector made of copper foil and a negative electrode active substance made of a carbon material and the like coating on a surface thereof. However, when the amount of copper nodules on the copper foil is excessive, the negative electrode active substance would be unevenly coated, or even the copper nodules would sometimes be stuck in the gaps of the coating die, causing the copper foil to break during coating, and thereby lowering the yield. The above issues are the current issues to be urgently resolved.
A copper foil may be divided into a rolled annealed copper foil or an electro deposited copper foil. The electrodeposited copper foil uses an aqueous solution of sulfuric acid and copper sulfate as an electrolyte, a titanium plate overlaid with an iridium element or an oxide thereof as a dimensionally stable anode (DSA), a titanium-made roller as a cathodic drum. A direct current is applied between the two poles, to electrically deposit the copper ions, which are in the electrolyte on the titanium-made roller, and then the deposited electrodeposited copper is peeled off from the surface of the titanium-made roller and continuously rolled up for producing the electrodeposited copper foil, wherein the surface of the electrodeposited copper foil in contact with the surface of the titanium-made roller is called “shiny surface (S surface),” and the reversed side is called “matte surface (M surface).” Usually, the roughness of the S surface of the electrodeposited copper foil depends upon the roughness of the surface of the titanium-made roller. Therefore, the roughness of the S surface is more constant, and the roughness of the M surface may be adjusted by controlling the conditions of the copper sulfate electrolyte.
Conventionally, an organic additive (for example, a low-molecular-weight gel (such as gelatin), hydroxymethyl cellulose (HEC) or polyethylene glycol (PEG)) or a sulfur-containing compound having a grain-refining effect (for example, sodium 3-mercaptopropane sulphonate (MPS), bis-(3-soldiumsulfopropyl disulfide) (SPS)) is added to a copper sulfate electrolyte to alter the crystalline phase of the electrodeposited copper foil.
Methods for reducing nodules are generally based on the approach of lowering the current density during electroplating to reduce the effect of point discharge. However, the decrease in the current density would bring about a reduction in the yield. Alternatively, the increase in the circulating quantity of the electrolyte, which allows the additive contained in the electrolyte to be more completely absorbed by activated carbon, would bring about an increase in the energy consumed during the production.
Accordingly, the development of an electrodeposited copper foil with reduced generation of nodules on a surface thereof, without compromising the production efficiency, is a current issue to be urgently resolved.